Conventionally, coating apparatuses using a rotary drum have been known as manufacturing apparatuses for medicine, food, and the like. For example, Patent Document 1 discloses an apparatus in which a rotary drum having a polygonal shape in cross-section (octagonal shape in this case) is rotated about a horizontal axis. Such a rotary drum is also referred to as a coating pan, and spray guns for supplying coating liquids are arranged in the drum. Powder and particle thrown into the rotary drum tumble in accordance with rotation of the drum. To surfaces of the rolling granular solids, coating liquids such as a sugar-coating liquid are sprayed from the spray guns. Simultaneously with spraying of the coating liquids, a hot air and a cool air are appropriately supplied into the rotary drum and exhausted therefrom. In this manner, formation and drying of coating layers are promoted.
When a sugar-coating process is performed in such a coating apparatus, first, objects to be processed as cores (such as tablets, hereinafter, the tablets are taken as a typical example) are housed in the rotary drum. After that, with the rotary drum being rotated, the coating liquids (sugar-coating liquid) and binder liquids are supplied into the drum so as to adhere to outer peripheries of the tablets. During the coating process, a hot air at a temperature of approximately 50 to 100° C. is appropriately blown to the tablets. The hot air causes the sugar-coating liquid to be evaporated and solidified on the surfaces of the tablets so that the coating layers are formed. Then, operations of adding the coating liquids and then drying the same are repeated. Through the repetitive operations, the coating layers are laminated on the outer peripheries of the tablets again and again. In this manner, sugar-coating layers are formed.
Patent Document 1: JP 05-309253 A
Patent Document 2: JP 08-173868 A
Patent Document 3: JP 07-241452 A
Patent Document 4: JP 2004-148292 A
However, in the coating apparatus as described above in which mouth-ring air supply is performed, an area of an air supply port is not sufficiently secured. Thus, there has been such a problem that a flow rate of the air supplied into the rotary drum is liable to become non-uniform. When airflow of the supplied air becomes non-uniform, a spray mist at the time of the coating process is disturbed, which leads to such a problem that the coating liquids and the binder liquids cannot be uniformly sprayed onto the tablets. Further, there has been also such a problem that, when spray patterns are disturbed, the spray mist dries before reaching the tablets, and the dried mist adheres to the drum and contaminates the same. In order to sufficiently reduce and stabilize the flow rate of the supplied air, it is necessary to elongate a mouth-ring straight barrel portion. However, when such a structure is employed, a distance from a mouth of the drum to a product layer increases, which leads to problems of marked deterioration of workability and an increase in size of the apparatus itself.
Meanwhile, a coating apparatus in which the mouth-ring air supply is not performed does not involve the problems as described above. However, for example, in a coating apparatus of an overall-punched structure in which an entire periphery of the straight barrel portion at the center of the drum is formed of punched metal, the air is supplied from an air supply duct provided on a right shoulder (in two to four o'clock directions) of the drum. Thus, the barrel portion of the drum is liable to be warmed. As a result, the sugar-coating liquid is solidified and adheres to an inner surface of the drum in some cases.
It is an object of the present invention to optimize, in the pan-type coating apparatus, the introduction path for the air to be supplied to objects to be processed so that airflow is stabilized and a coating performance is enhanced.